Characterization and quantification of within-year variation of snow-cover elevation in mountainous regions, eastern Tibet

Fluctuating snow-covered elevation(FSCE) was conceptualized and proposed to characterize within-year variation of the border between snow-covered area and snow-free area in mountainous regions.Two parameters,namely median of the snow-free period(Tm) and duration of snow-free period(DT),were defined to quantify FSCE.A regression model of FSCE was developed for the Lhasa River basin,Niyang River basin and Changdu Prefecture in Eastern Tibet.Statistical analyses of the snow-products data with a spatial resolution of 25 km×25 km show that: 1) Tm correlates insignificantly with geographical and topographic factors,having the yearly mean value of July 31;2) DT correlates significantly with the average elevation of the snow-products cell,having the yearly mean value of nearly five months(i.e.,151 days);3) in the region snow melting begins in last April and snow cover begins in mid November;from last June to mid September there is a snow-free period and from December to March in the next year there is a snow-cover period.In addition,snow-products with higher spatial resolution will be helpful to characterize FSCE in smaller spatial scales.